1. Field of the Invention
The present invention relates to manufacture of electroluminescent elements using an inorganic material. In addition, the present invention relates to light emitting devices and electronic devices using the electroluminescent elements.
2. Description of the Related Art
In recent years, liquid crystal display devices and electroluminescent display devices which are formed by integrating thin film transistors (hereinafter also referred to as TFTs) over a glass substrate have been developed. As for any of these display devices, thin film transistors are formed over a glass substrate using a thin film formation technique, and display elements such as liquid crystal elements or light emitting elements (electroluminescent (hereinafter also referred to as EL) elements) are formed over various circuits including the thin film transistors, thereby functioning as display devices.
Light emitting elements utilizing electroluminescence can be classified according to whether a light emitting material is an organic compound or an inorganic compound. In general, the former are referred to as organic EL elements, and the latter are referred to as inorganic EL elements.
The inorganic EL elements are classified according to their element structures into dispersion-type inorganic EL elements and thin-film inorganic EL elements. Since the inorganic EL elements obtain EL light emission by application of an AC voltage, an insulating layer to be a dielectric is necessary. In addition to a high dielectric constant, a high withstand voltage and the like are required for the insulating layer, and there is a method in which the insulating layer is formed with a stacked structure in order to meet the characteristic requirements (for example, refer to Reference 1: Japanese Published Patent Application No. 2003-77677). Furthermore, the density of a film is increased for increasing the withstand voltage, the internal stress of the film is also increased and peeling at an interface may be generated. Therefore, there is a method in which a film with a low stress is interposed as a buffer layer in order to relieve the internal stress, in forming a stacked structure.